A1,
A2,
B,
C1,
C2,
D,
E,
F,
G-H,
I-K,
L,
M,
N,
O,
P1,
P2,
Q-R,
S,
T,
U-V,
W-Z
Unipen Pharmacology, Pharmacokinetics, Studies, Metabolism - Nafcillin Sodium
Unipen Pharmacology, Pharmacokinetics, Studies, Metabolism - Nafcillin Sodium
CLINICAL PHARMACOLOGY
MICROBIOLOGY
Penicillinase-resistant penicillins exert a bactericidal
action against penicillin-susceptible
microorganisms during the state
of active multiplication. All penicillins inhibit the biosynthesis
of the bacterial cell wall.
The drugs in this class
are highly resistant to inactivation
by staphylococcal penicillinase and are active against penicillinase-producing
and non penicillinase-producing strains of Staphylococcus aureus.
The penicillinase- resistant penicillins are active in vitro
against a variety of other bacteria.
Susceptibility Plate Testing: Quantitative methods of susceptibility
testing that require measurement of zone
diameters or minimal
inhibitory concentrations (MIC's) give the most precise estimates
of antibiotic susceptibility.
One such procedure
has been recommended for use with discs to test
susceptibility to this class
of drugs. Interpretations correlate diameters on the disc test with
MIC values. A penicillinase-
resistant class disc
may be used to determine microbial susceptibility to cloxacillin,
dicloxacillin, methicillin, nafcillin, and oxacillin. With this
procedure, employing a 5 microgram methicillin sodium
disc, a report from the
laboratory of ''susceptible'' (zone of at least 14 mm) indicates
that the infecting organism
is likely to respond to therapy. A report
of ''resistant'' (zone of less than 10 mm) indicates that the infecting
organism is not likely
to respond to therapy. A report
of ''intermediate susceptibility'' (zone of 10 to 13 mm) suggests
that the organism might
be susceptible if
high doses of the antibiotic are used, or if the infection
is confined to tissues and fluids (e.g., urine), in which high antibiotic
levels are attained.
In general, all staphylococci
should be tested against the penicillin G disc
and against the methicillin disc. Routine methods of antibiotic
susceptibility testing may fail to detect strains of organisms resistant
to the penicillinase- resistant penicillins. For this reason, the
use of large inocula and 48-hour incubation
periods may be necessary to obtain accurate susceptibility studies
with these antibiotics. Bacterial strains which are resistant to
one of the penicillinase- resistant penicillins should be considered
resistant to all of the drugs in the class.
PHARMACOKINETICS
Intramuscular injections of Nafcillin Sodium, USP 1 gram
produced peak serum levels in 0.5 to 1 hour of 7.61 µg/mL.
The degree of protein
binding reported has been 89.9 + /- 1.5%. With normal
doses Nafcillin is found in therapeutic
concentrations in the pleural, bile, and amniotic fluids. Insignificant
concentrations are found in the cerebrospinal
fluid and aqueous humor.
Blood concentrations may be tripled by the concurrent use of probenecid.
Clinical studies with nafcillin sodium
in infants under three days of age
and prematures have revealed higher blood
levels and slower rates of urinary excretion
than in older children and adults. A high concentration
of nafcillin sodium is
excreted via the bile. About
30% of an intramuscular
dose is excreted in the
urine.
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